Synthesis of statistical microgels by means of controlled radical polymerisation

ABSTRACT

The invention relates to a method of preparing statistical microgels. The inventive method comprises a step involving the radical polymerisation of a composition containing: at least one monoethylenically-unsaturated monomer, at least one multiethylenically-unsaturated monomer, a free radical source and a control agent. The invention also relates to first generation microgels thus prepared and all the compounds resulting from said microgels (next-generation microgels).

This application is an application under 35 U.S.C. Section 371 ofInternational Application Number PCT/FR2003/002303, filed on Jul. 21,2003.

The present invention relates to a novel radical polymerization processwhich gives access to random microgels and to the random microgels thusobtained.

Random microgels represent a particular class of polymers regarded asintermediate between the family of branched polymers and that of polymernetworks which are macroscopically crosslinked, known as macrogels(Murray, M. J. and Snowden, M. J., Adv. Colloid Interface Sci., 1995,54, 73). Thus, random macrogels may be defined as being amacroscopically soluble assembly of intramolecularly crosslinkedmacromolecules exhibiting a globular structure with a colloidal sizetypically of between 10 and 1000 nm (Funke, W., Adv. Polym. Sci., 1998,136, 139) and with a molar mass of the order of 10⁴ to 10⁶ g.mol⁻¹.Other terms, including “microparticles”, “microspherical hydrogels”,“nanoparticles”, “latex particles”, and the like, have been proposed todescribe the structure of random microgels.

In addition to their solubility in an appropriate solvent, mention maybe made, among other advantages of random microgels with respect tomacrogels, of their greater ease of purification by conventionalprecipitation techniques.

Microgels are known to have multiple properties, possibly different fromthose of the corresponding macrogels and linear homopolymers. Forexample, the viscosity in dilute solution of a microgel is lower thanthat of an equivalent polymer with a linear structure and the filmsformed from a random microgel exhibit better mechanical propertieswithout the properties desired, such as, for example, the gloss or thedurability, being affected (Ishikura, S. et al., Prog. Org. Coat., 1988,15, 373).

Random microgels are used as additives to reduce the viscosity ofsolvent-based formulations or formulations in a molten medium(processing aid) or else to improve the impact strength of materials.Their use makes it possible to increase the solids content of theseformulations with the advantage of reducing solvent emissions andmaintaining the viscosity. Mention may be made, among the fields ofapplication concerned, of paints, oil wells or wastewater treatment.

The processes for the preparation of these random microgels can becategorized into several groups. The first corresponds to thecopolymerization in very dilute solution of a mixture of monomerscomprising at least one crosslinking monomer (Staudinger, H. andHusemann, E., Chem. Ber., 1935, 68, 1618; Stöver, D. H. et al.,Macromolecules, 2002, 35, 2728). In such a case, diluting promotes theintramolecular crosslinking reactions at the expense of theintermolecular crosslinking reactions which, for their part, result inthe formation of an insoluble and infusible macrogel. Provision has alsobeen made for a solution radical copolymerization process involving atleast one crosslinking monomer in the presence of a chain-transfer agentof mercaptan type, so as to avoid the formation of the macrogel(Sherrington, D S. C., Polymer, 2000, 41).

The second method for the preparation of random macrogels consists incopolymerizing a mixture of monomers comprising at least onecrosslinking monomer using an emulsion polymerization process(Antonietti, M., Angew. Chem. Int. Ed., 1988, 27, 1743). In this case,the intermolecular crosslinking reactions are restricted as a result ofthe compartmentalization in micelles of the macromolecules being formed.

Recourse is generally had to radical polymerization in order to obtainpolymer chains connected to one another via crosslinking pointsresulting from the crosslinking monomer(s).

However, other methods for preparing random microgels have beendeveloped, in particular that proceeding by means of ionicpolymerization. Thus, the addition of the divinylbenzene used ascoupling agent to “living” polystyrene chains prepared by solutionanionic polymerization results in a star-shaped random microgel composedof a crosslinked core and of polystyrene arms around the central portion(Rempp, P. et al., Compt. Rend. Acad. Sci., 1966, 262, 726).Alternatively, the anionic polymerization in dilute solution ofdivinylbenzene results in a microgel carrying carbanionic sites fromwhich it is possible to grow polystyrene chains in order to obtain astar-shaped polymer (Eschwey, H. and Burchard, W., Polymer, 1975, 16,180). Other coupling agents have been used to obtain random microgels byanionic polymerization, in particular those based on chlorosilane groups(Antonietti, M. et al., Macromolecules, 1989, 22, 2802). More recently,star-shaped random microgels have been prepared by “living” cationicpolymerization (Higashimura, T. et al., Macromolecules, 1996, 29, 1772).

Recently, a process for the synthesis of star-shaped random microgelsfrom the coupling of linear polymer chains, preformed by controlledradical polymerization, with a polyethylenically unsaturated monomer hasbeen proposed. The techniques used for this purpose may involve controlagents, such as nitroxyls, used as counterradicals (T. Long, J. Polym.Sci. Part A.: Polym. Chem., 2001, 39, 216), transition metal complexesused in the Atom Transfer Radical Polymerization (ATRP) technology(Matyjaszewski, K., Macromolecules, 1999, 32, 4482) or else agentscarrying thiocarbonylthio groups, such as dithioesters, in a reversibleaddition-fragmentation process (WO 00/0293). In this case, thereactivatable groups resulting from the linear precursors are found atthe core of the star polymers thus formed.

In the continuation of the description, the terms “first-generationrandom microgels” and “second-generation random microgels” are used torespectively describe random microgels composed of a polymer comprisingchain ends which can be activated by reversible transfer or bytermination and the products composed of the first-generation randommicrogel at the core and of polymer arms extending from the chain endswhich can be activated of said central portion.

Furthermore, the term “polymer comprising chain ends which can beactivated” includes any polymer comprising one (or more) halogen orpseudohalogen group(s) which is obtained by ARTP, and also any polymercarrying a thiocarbonylthio group (dithiocarbamate, dithiocarbonate,trithiocarbonate, dithioester, thioether-thione, dithiocarbazate) at thechain end which is obtained by a reversible addition-fragmentationprocess.

Mention may be made, as an example illustrative of the ATRP process, ofpatent WO 96/30421. Patent applications WO 98/01478 on behalf of Dupontde Nemours and WO 99/35178 on behalf of Rhodia Chimie disclose the useof addition-fragmentation control (or reversible transfer) agents ofdithioester RSC═SR′ type for the synthesis of controlled-architecturecopolymers. Another family of control agents, the xanthates RSC═SOR′,has been disclosed in patent applications WO 98/58974, WO 00/75207 andWO 01/42312 of Rhodia Chimie as precursors of block copolymers. Thecontrol of radical polymerization by dithiocarbamates RS(C═S)NR₁R₂ hasalso been disclosed recently in patent applications WO 99/35177 onbehalf of Rhodia and WO 99/31144 on behalf of Dupont de Nemours. Inaddition, thioether-thione compounds have been disclosed as controlagents for radical polymerization in patent application FR 2 794 464,filed on behalf of Rhodia Chimie. In addition, dithiocarbazate compoundshave been disclosed as control agents for radical polymerization inpatent application WO 02/26836, filed on behalf of Symyx.

A process for the preparation of random microgels by the controlledradical route employing nitroxyl radicals as control agent for thecopolymerization of tert-butylstyrene and divinylbenzene has beendisclosed (Solomon, Polymer, 2001, 42, 5987). However, this method islimited to the family of the styrene monomers and furthermore requiresrelatively high polymerization temperatures (110 to 130° C.).

One aim of the present invention is thus to provide a novel process forthe synthesis of microgels by the controlled radical route which doesnot exhibit the disadvantages or limitations of the processes for thesynthesis of random microgels provided to date.

Another aim of the invention is to provide a process for the synthesisof first-generation random microgels during which the degree ofbranching, the number-average molar masses and the density of surfacereactive functional groups can be varied and consequently the shape andthe size of said random microgels can be varied.

Another aim is to provide a controlled radical polymerization processwhich is simple to carry out and which makes it possible to result inrandom microgels of a higher generation starting from thefirst-generation random microgels.

Another aim is to provide a process which makes possible access tostar-shaped second-generation random microgels, the branches of whichcomprise reactivatable groups at their ends. These groups canadvantageously be modified so as to functionalize the arms of thestar-shaped random microgels.

Another aim of the invention is to provide a process for the synthesisof random microgels of a higher generation than the first, during whichthe degree of branching, the number-average molar masses and the densityof surface reactive functional groups can be varied and consequently theshape and the size of said random microgels can be varied.

Another aim is to provide a controlled radical polymerization processwhich can be applied to a very broad range of monomers, in comparisonwith the known techniques of the prior art.

In the context of the present invention, the synthesis of randommicrogels is carried out by resorting to the ATRP process or to theprocess involving thiocarbonylthio or thiophosphate control agentsoperating in a reversible addition-fragmentation process.

These aims and others are achieved by the present invention, whichrelates first of all to a process for the preparation of“first-generation” random microgels which comprises a stage ofcontrolled radical polymerization of a composition comprising:

-   -   at least one monoethylenically unsaturated monomer,    -   at least one polyethylenically unsaturated monomer,    -   a source of free radicals, and    -   a control agent.

The ethylenically unsaturated monomers of use in the process of thepresent invention are all the monomers which polymerize in the presenceof the control agent to give active polymer chains.

These ethylenically unsaturated monomers are, for example:

-   -   styrene and styrene derivatives, such as α-methylstyrene or        vinyltoluene,    -   carboxylic acid vinyl esters, such as vinyl acetate, VINYL        VERSATATE®, also known as vinyl neodecanoate, or vinyl        propionate,    -   vinyl and vinylidene halides,    -   unsaturated ethylenic mono- and dicarboxylic acids, such as        acrylic acid, methacrylic acid, itaconic acid, maleic acid or        fumaric acid, and the monoalkyl esters of the dicarboxylic acids        of the type mentioned with alkanols preferably having 1 to 4        carbon atoms and their N-substituted derivatives,    -   amides of unsaturated carboxylic acids, such as acrylamide,        methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide        or N-alkylacrylamides,    -   ethylenic monomers comprising a sulfonic acid group and its        alkali metal or ammonium salts, for example vinylsulfonic acid,        vinylbenzenesulfonic acid,        .alpha.-acrylamidomethylpropanesulfonic acid or 2-sulfoethylene        methacrylate,    -   amides of vinylamine, in particular vinylformamide,        vinylacetamide, N-vinylpyrrolidone and N-vinylcaprolactam,    -   unsaturated ethylenic monomers comprising a secondary, tertiary        or quaternary amino group or a heterocyclic group comprising        nitrogen, such as, for example, vinylpyridines, vinylimidazole,        aminoalkyl (meth)acrylates and aminoalkyl(meth)acrylamides, such        as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate,        di(tert-butyl)aminoethyl acrylate, di(tert-butyl)aminoethyl        methacrylate, dimethylaminomethylacrylamide or        dimethylamino-methylmethacrylamide, or zwitterionic monomers,        such as, for example, sulfopropyl(dimethyl)-aminopropyl        acrylate,    -   (meth)acrylic esters, such as glycidyl acrylate or glycidyl        methacrylate,    -   vinyl nitrites,    -   monomers comprising at least one boronate functional group or        one precursor, for example chosen from acryloylbenzeneboronic        acid, methacryloylbenzeneboronic acid, 4-vinylbenzene-boronic        acid, 3-acrylamidophenylboronic acid or        3-methacrylamidophenylboronic acid, alone or as mixtures, or in        the form of salts,    -   monomers comprising phosphonates, for example chosen from        N-methacrylamidomethylphosphonic acid ester derivatives, in        particular the n-propyl ester (RN 31857-11-1), the methyl ester        (RN 31857-12-2), the ethyl ester (RN 31857-13-3), the n-butyl        ester (RN 31857-14-4) or the isopropyl ester (RN 51239-00-0),        and their phosphonic monoacid and diacid derivatives, such as        N-methacrylamido-methylphosphonic diacid (RN 109421-20-7);        N-methacrylamidoethylphosphonic acid ester derivatives, such as        N-methacrylamidoethylphosphonic acid dimethyl ester (RN        266356-40-5) or N-methacrylamidoethylphosphonic acid        di(2-butyl-3,3-dimethyl) ester (RN 266356-45-0), and their        phosphonic monoacid and diacid derivatives, such as        N-methacrylamidoethylphosphonic diacid (RN 80730-17-2);        N-acrylamidomethylphosphonic acid ester derivatives, such as        N-acrylamido-methylphosphonic acid dimethyl ester (RN        24610-95-5), N-acrylamidomethylphosphonic acid diethyl ester (RN        24610-96-6) or bis(2-chloropropyl) N-acrylamidomethylphosphonate        (RN 50283-36-8), and their phosphonic monoacid and diacid        derivatives, such as N-acrylamidomethylphosphonic acid (RN        151752-38-4); the vinylbenzylphosphonate dialkyl ester        derivatives, in particular the di(n-propyl) (RN 60181-26-2),        di(isopropyl) (RN 159358-34-6), diethyl (RN 726-61-4), dimethyl        (RN 266356-24-5), di(2-butyl-3,3-dimethyl) (RN 266356-29-0) and        di(t-butyl) (RN 159358-33-5) ester derivatives, and their        phosphonic monoacid and diacid alternative forms, such as        vinylbenzylphosphonic diacid (RN 53459-43-1); diethyl        2-(4-vinyl-phenyl)ethanephosphonate (RN 61737-88-0);        dialkylphosphonoalkyl acrylate and methacrylate derivatives,        such as 2-(acryloyloxy)ethyl-phosphonic acid dimethyl ester (RN        54731-78-1) and 2-(methacryloyloxy)ethylphosphonic acid dimethyl        ester (RN 22432-83-3), 2-(methacryloyloxy)methyl-phosphonic acid        diethyl ester (RN 60161-88-8),        2-(methacryloyloxy)methylphosphonic acid dimethyl ester (RN        63411-25-6), 2-(methacryloyloxy)propyl-phosphonic acid dimethyl        ester (RN 252210-28-9), 2-(acryloyloxy)methylphosphonic acid        diisopropyl ester (RN 51238-98-3) or        2-(acryloyloxy)ethyl-phosphonic acid diethyl ester (RN        20903-86-0), and their phosphonic monoacid and diacid        alternative forms, such as 2-(methacryloyloxy)ethylphosphonic        acid (RN 80730-17-2), 2-(methacryloyloxy)methyl-phosphonic acid        (RN 87243-97-8), 2-(meth-acryloyloxy)propylphosphonic acid (RN        252210-30-3), 2-(acryloyloxy)propylphosphonic acid (RN        254103-47-4) and 2-(acryloyloxy)ethylphosphonic acid;        vinylphosphonic acid, optionally substituted by cyano, phenyl,        ester or acetate groups, vinylidenephosphonic acid, in the        sodium salt form or the form of its isopropyl ester, or        bis(2-chloroethyl)vinylphosphonate, it being possible for these        monomers comprising a phosphonic mono- or diacid functional        group to be used in the partially or completely neutralized        form, optionally neutralized by an amine, for example        dicyclohexylamine,    -   monomers chosen from the phosphate analogs of the        phosphonate-comprising monomers described above, the monomers        then comprising a —C—O—P— sequence in comparison with the —C—P—        sequence of the phosphonates, and    -   monomers carrying an alkoxysilane group chosen from        trimethoxysilypropyl methacrylate, triethoxysilylpropyl        methacrylate, tributoxy-silylpropyl methacrylate,        dimethoxymethylsilylpropyl methacrylate,        diethoxymethylsilylpropyl methacrylate,        dibutoxymethylsilylpropyl methacrylate,        diisopropoxymethylsilylpropyl methacrylate, dimethoxysilylpropyl        methacrylate, diethoxysilylpropyl methacrylate,        dibutoxysilyl-propyl methacrylate, diisopropoxysilylpropyl        methacrylate, trimethoxysilylpropyl methacrylate,        triethoxysilylpropyl methacrylate, tributoxysilylpropyl        methacrylate, trimethoxysilypropyl acrylate,        triethoxysilyl-propyl acrylate, tributoxysilylpropyl acrylate,        dimethoxymethylsilylpropyl acrylate, diethoxy-methylsilylpropyl        acrylate, dibutoxymethylsilyl-propyl acrylate,        diisopropoxymethylsilylpropyl acrylate, dimethoxysilylpropyl        acrylate, diethoxysilylpropyl acrylate, dibutoxysilylpropyl        acrylate, diisopropoxysilylpropyl acrylate,        trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate or        tributoxysilylpropyl acrylate.

The term “(meth)acrylic esters” denotes the esters of acrylic acid andof methacrylic acid with hydrogenated or fluorinated C₁-C₁₂ alcohols,preferably C₁-C₈ alcohols. Mention may be made, among the compounds ofthis type, of: methyl acrylate, ethyl acrylate, propyl acrylate, n-butylacrylate, isobutyl acrylate, 2-ethylhexyl acrylate, t-butyl acrylate,methyl methacrylate, ethyl methacrylate, n-butyl methacrylate orisobutyl methacrylate.

The vinyl nitriles include more particularly those having from 3 to 12carbon atoms, such as, in particular, acrylonitrile andmethacrylonitrile.

Use is preferably made, for the preparation of a polyvinylamine block,as ethylenically unsaturated monomers, of amides of vinylamine, forexample vinylformamide or vinylacetamide. The polymer obtained is thenhydrolyzed at acidic or basic pH.

Use is preferably made, for the preparation of a poly(vinyl alcohol)block, as ethylenically unsaturated monomers, of carboxylic acid vinylesters, such as, for example, vinyl acetate. The polymer obtained isthen hydrolyzed at acidic or basic pH.

The ethylenically unsaturated monomers used in the preparation of themicrogels are preferably chosen from styrene monomers, vinyl esters,neutral or charged hydrophilic acrylates, hydrophobic acrylates, neutralor charged hydrophilic methacrylates, hydrophobic methacrylates,hydrophilic or hydrophobic and neutral or charged acrylamido derivativesor hydrophilic or hydrophobic and neutral or charged methacrylamidoderivatives.

The types and amounts of polymerizable monomers employed according thepresent invention vary according to the specific final application forwhich the polymer is intended. These variations are well known and canbe easily determined by a person skilled in the art.

These ethylenically unsaturated monomers can be used alone or asmixtures.

The polyethylenically unsaturated monomers of use in the process of thepresent invention are all the monomers which polymerize in the presenceof the control agent to give “first-generation” and “higher-generation”microgels.

The polyethylenically unsaturated monomers are chosen from organiccompounds comprising at least two ethylenic unsaturations and at most 10unsaturations and which are known as being reactive by the radicalroute.

Preferably, these monomers exhibit two or three ethylenic unsaturations.

Thus, mention may in particular be made of acrylic, methacrylic,acrylamido, methacrylamido, vinyl ester, vinyl ether, diene, styrene,α-methylstyrene and allyl derivatives. These monomers can also includefunctional groups other than ethylenic unsaturations, for examplehydroxyl, carboxyl, ester, amide, amino, substituted amino, mercapto,silane, epoxy or halo functional groups.

The monomers belonging to these families are divinylbenzene anddivinylbenzene derivatives, vinyl methacrylate, methacrylic acidanhydride, allyl methacrylate, ethylene glycol dimethacrylate, phenylenedimethacrylate, diethylene glycol dimethacrylate, triethylene glycoldimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol200 dimethacrylate, polyethylene glycol 400 dimethacrylate,1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate,1,6-hexanediol dimethacrylate, 1,12-dodecanediol dimethacrylate,1,3-glycerol dimethacrylate, diurethane dimethacrylate ortrimethylolpropane trimethacrylate. For the family of the polyfunctionalacrylates, mention may in particular be made of vinyl acrylate,bisphenol A epoxy diacrylate, dipropylene glycol diacrylate,tripropylene glycol diacrylate, polyethylene glycol 600 diacrylate,ethylene glycol diacrylate, diethylene glycol diacrylate, triethyleneglycol diacrylate, tetraethylene glycol diacrylate, neopentyl glycolethoxylate diacrylate, butanediol diacrylate, hexanediol diacrylate,aliphatic urethane diacrylate, trimethylolpropane triacrylate,trimethylolpropane ethoxylate triacrylate, trimethylolpropanepropoxylate triacrylate, glycerol propoxylate triacrylate, aliphaticurethane triacrylate, trimethylolpropane tetraacrylate ordipentaerythritol pentaacrylate. As regards the vinyl ethers, mentionmay in particular be made of vinyl crotonate, diethylene glycol divinylether, 1,4-butanediol divinyl ether or triethylene glycol divinyl ether.For the allyl derivatives, mention may in particular be made of diallylphthalate, diallyldimethylammonium chloride, diallyl maleate, sodiumdiallyloxyacetate, diallylphenylphosphine, diallyl pyrocarbonate,diallyl succinate, N,N′-diallyl-tartardiamide,N,N-diallyl-2,2,2-trifluoroacetamide, the allyl ester ofdiallyloxyacetic acid, 1,3-diallylurea, triallylamine, triallyltrimesate, triallyl cyanurate, triallyl trimellitate or1,3,5-triallyltriazine-2,4,6(1H,3H,5H)-trione. For the acrylamidoderivatives, mention may in particular be made ofN,N′-methylenebisacrylamide, N,N′-methylenebismethacrylamide,glyoxalbisacrylamide or diacrylamidoacetic acid. As regards the styrenederivatives, mention may in particular be made of divinylbenzene and1,3-diisopropenylbenzene. In the case of the diene monomers, mention mayin particular be made of butadiene, chloroprene and isoprene.

Preference is given, as polyethylenically unsaturated monomers, toN,N′-methylenebisacrylamide, divinylbenzene, ethylene glycol diacrylateor trimethylolpropane triacrylate.

These polyethylenically unsaturated monomers can be used alone or asmixtures.

The types and amounts of polyethylenically unsaturated monomers employedaccording to the present invention vary according to the specific finalapplication for which the random microgel is intended. These variationsare easily determined by a person skilled in the art.

The molar fraction of polyethylenically unsaturated monomers withrespect to the monoethylenically unsaturated monomers is between 0.001and 1. Preferably, the molar fraction is between 0.01 and 1.

The process of the invention is in all cases carried out in the presenceof a source of free radicals. However, for some monomers, such asstyrene, the free radicals which make it possible to initiate thepolymerization can be generated by the monoethylenically unsaturatedmonomer at sufficiently high temperatures, generally of greater than100° C. It is not, in this case, necessary to add a source of additionalfree radicals.

In the case where a process according to the invention is carried out byliving radical polymerization of reversible transfer byaddition-fragmentation of thiocarbonylthio or thiophosphate compoundstype, the source of free radicals which is of use is generally a radicalpolymerization initiator. The radical polymerization initiator can bechosen from the initiators conventionally used in radicalpolymerization. It can, for example, be one of the following initiators:

-   -   hydrogen peroxides, such as tertiary-butyl hydroperoxide, cumene        hydroperoxide, t-butyl peroxyacetate, t-butyl peroxybenzoate,        t-butyl peroxyoctoate, t-butyl peroxyneodecanoate, t-butyl        peroxyisobutyrate, lauroyl peroxide, t-amyl peroxypivalate,        t-butyl peroxypivalate, dicumyl peroxide, benzoyl peroxide,        potassium persulfate or ammonium persulfate,    -   azo compounds, such as: 2,2′-azobis(iso-butyronitrile),        2,2′-azobis(2-butanenitrile), 4,4′-azobis(4-pentanoic acid),        1,1′-azobis(cyclohexane-carbonitrile),        2-(t-butylazo)-2-cyanopropane,        2,2′-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl)propionamide,        2,2′-azobis(2-methyl-N-hydroxyethyl]propionamide,        2,2′-azobis(N,N′-dimethylene-isobutyramidine) dichloride,        2,2′-azobis(2-amidino-propane)dichloride,        2,2′-azobis(N,N′-dimethylene-isobutyramide),        2,2′-azobis(2-methyl-N-[1,1-bis-(hydroxymethyl)-2-hydroxyethyl]propionamide),        2,2′-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]-propionamide),        2,2′-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] or        2,2′-azobis(isobutyramide) dihydrate,    -   redox systems comprising combinations such as:    -   mixtures of hydrogen peroxide, alkyl peroxide, peresters,        percarbonates and the like and of any of the iron salts,        titanous salts, zinc formaldehydesulfoxylate or sodium        formaldehydesulfoxylate, and reducing sugars,    -   alkali metal or ammonium persulfates, perborates or        perchlorates, in combination with an alkali metal bisulfite,        such as sodium metabisulfite, and reducing sugars, and    -   alkali metal persulfates in combination with an arylphosphinic        acid, such as benzenephosphonic acid and other similar        compounds, and reducing sugars.

According to one embodiment for the process for the preparation ofrandom microgels according to the invention, the amount of initiator tobe used is determined so that the amount of radicals generated is atmost 50 mol %, preferably at most 20 mol %, with respect to the amountof control agent.

Mention may in particular be made, among the control agents which can beused in the radical polymerization by a process of reversible transferby addition-fragmentation of thiocarbonylthio compounds type to preparethe first-generation microgel, of reversible addition-fragmentationagents of dithioester type of formula RSC═SR′, as disclosed in patentapplications WO 98/01478 and WO 99/35178, xanthates RSC═SOR′, asdisclosed in patent applications WO 98/58974, WO 00/75207 and WO01/42312, dithiocarbamates of formula RS(C═S)NR₁R₂, such as thosedisclosed in patent applications WO 99/35177 and WO 99/31144,thioether-thione compounds, such as those disclosed in patentapplication FR 2 794 464, filed on behalf of Rhodia Chimie, ordithiocarbazate compounds, such as those disclosed in patent applicationWO 02/26836, filed on behalf of Symyx.

Thus, the control agents which can be used in the radical polymerizationby a process of reversible transfer by addition-fragmentation ofthiocarbonylthio compounds type are compounds which can be of followingformula (A):

in which:

-   -   Z represents:    -   a hydrogen atom,    -   a chlorine atom,    -   an optionally substituted alkyl radical or an optionally        substituted aryl radical,    -   an optionally substituted heterocycle,    -   an optionally substituted alkylthio radical,    -   an optionally substituted arylthio radical,    -   an optionally substituted alkoxy radical,    -   an optionally substituted aryloxy radical,    -   an optionally substituted amino radical,    -   an optionally substituted hydrazine radical,    -   an optionally substituted alkoxycarbonyl radical,    -   an optionally substituted aryloxycarbonyl radical,    -   a carboxyl or optionally substituted acyloxy radical,    -   an optionally substituted aroyloxy radical,    -   an optionally substituted carbamoyl radical,    -   a cyano radical,    -   a dialkyl- or diaryl-phosphonato radical,    -   a dialkyl-phosphinato or diaryl-phosphinato radical, or    -   a polymer chain,    -   R₁ represents:        -   an optionally substituted alkyl, acyl, aryl, aralkyl,            alkenyl or alkynyl group,        -   an optionally substituted, aromatic, saturated or            unsaturated, carbon ring or heterocycle,        -   a polymer chain.

The R₁ or Z groups, when they are substituted, can be substituted byoptionally substituted phenyl groups, optionally substituted aromaticgroups, saturated or unsaturated carbon rings, saturated or unsaturatedheterocycles, or the following groups: alkoxycarbonyl or aryloxycarbonyl(—COOR), carboxyl (—COOH), acyloxy (—O₂CR), carbamoyl (—CONR₂), cyano(—CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl,arylalkylcarbonyl, phthalimido, maleimido, succinimido, amidino,guanidino, hydroxyl (—OH), amino (—NR₂), halogen, perfluoroalkylC_(n)F_(2n+1), allyl, epoxy, alkoxy (—OR), S-alkyl, S-aryl, groupsexhibiting a hydrophilic or ionic nature, such as alkaline salts ofcarboxylic acids or alkaline salts of sulfonic acids, poly(alkyleneoxide) (PEO, PPO) chains, cationic substituents (quaternary ammoniumsalts), R representing an alkyl or aryl group, or a polymer chain.

According to a specific embodiment, R₁ is a substituted orunsubstituted, preferably substituted, alkyl group.

The compounds (A) of use in the present invention are, for example, thecompounds in which R₁ is chosen from:

-   -   —CH₂C₆H₅    -   —CH(CH₃)(CO₂Et)    -   —CH(CH₃)(C₆H₅)    -   —CH(CO₂Et)₂    -   —C(CH₃)(CO₂Et)(S—C₆H₅)    -   —C(CH₃)₂(C₆H₅)    -   —C(CH₃)₂CN

in which Et represents an ethyl group and Ph represents a phenyl group.

The optionally substituted alkyl, acyl, aryl, aralkyl or alkynyl groupsgenerally exhibit 1 to 20 carbon atoms, preferably 1 to 12 carbon atomsand more preferably 1 to 9 carbon atoms. They can be linear or branched.They can also be substituted by oxygen atoms, in the form in particularof esters, sulfur atoms or nitrogen atoms.

Mention may in particular be made, among alkyl radicals, of the methyl,ethyl, propyl, butyl, pentyl, isopropyl, tert-butyl, pentyl, hexyl,octyl, decyl or dodecyl radicals.

The alkynyl groups are radicals generally of 2 to 10 carbon atoms; theyexhibit at least one ethylenic unsaturation, such as the acetylenylradical.

The acyl group is a radical generally exhibiting from 1 to 20 carbonatoms with a carbonyl group.

Mention may in particular be made, among aryl radicals, of theoptionally substituted phenyl radical, in particular substituted by anitro or hydroxyl functional group.

Mention may in particular be made, among aralkyl radicals, of theoptionally substituted benzyl or phenethyl radical, in particularsubstituted by a nitro or hydroxyl functional group.

When R₁ or Z is a polymer chain, this polymer chain can result from aradical or ionic polymerization or can result from a polycondensation.

In the context of the present invention, preference is given to thefollowing control agents: xanthate, dithiocarbamate, dithioester anddithiocarbazate compounds.

Use is advantageously made, as control agent, of xanthate compounds.

When the first-generation random microgels composed of polymerscomprising halogen or pseudohalogen chain ends are obtained by the AtomTransfer Radical Polymerization (ATRP) process, the control agent of thepolymerization is a transition metal in combination with a ligand actingas catalyst of the polymerization.

Mention may be made, as examples of transition metal in combination witha ligand acting as catalyst for the polymerization, of the complexes ofthe following types: CuX/2,2′-bipyridyl, CuX/Schiff base,CuX/N-alkyl-2-pyridylmethanimine,CuX/tris[2-(dimethylamino)-ethyl]amine,CuX/N,N,N′,N″,N″-pentamethyldiethylenetri-amine,CuX/tris[(2-pyridyl)methyl]amine, Mn(CO)₆, RuX_(x)(PPh₃)₃,NiX[(o-o′-CH₂NMe₂)₂C₆H₃], RhX(PPh₃)₃, NiX₂(PPh₃)₂ and FeX₂/P(n-Bu)₃,where X is a halogen or a pseudohalogen.

An aluminum trialkoxide Al(OR)₃ can be employed as additive to activatethe polymerization.

A detailed list of transition metals and associated ligands is disclosedin the document WO 96/30421, from page 22, line 6, to page 26, line 8.

BRIEF DESCRIPTION OF THE DRAWINGS

The assumed mechanism of the ATRP process is shown in the schemepresented in FIG. 1.

The metal complex (Mt^(n)X) captures the halogen atom of the organichalide (R—X) to form the R. radical and the oxidized metallic entityMt^(n+1)X₂. In the following stage, R. reacts with the monomer M to forma new radical active entity RM.

The reaction between RM. and Mt^(n+1)X₂ results in the formation of apotentially reactivatable entity RMX and, at the same time, the metalliccompound in its reduced form Mt^(n)X. The latter can again react with RXand can promote a new redox cycle.

In the presence of a large excess of monomer M, the RM_(n)X entities aresufficiently reactive with respect to the Mt^(n)X complex to promote acertain number of activation/deactivation cycles, that is to say a“living” or controlled radical polymerization reaction.

Details with regard to the mechanism of this process are described inthe document Macromolecules, 1995, 28, 7901.

In the case where a process according to the invention via livingradical polymerization of ATRP type is employed, the source of freeradicals which is of use is generally an organic halide activated by theredox route.

The organic halides acting as source of free radicals in the ATRPprocess are, for example:

-   -   an arenesulfonyl halide or alkanesulfonyl halide of formula        RSO₂X, where X is a chlorine atom, a bromine atom or an iodine        atom and R is an aryl, alkyl, substituted alkyl or substituted        aryl group. A list of the R groups which come within the scope        of the invention is given, for example, in the document WO        98/20050.    -   a halide of formula R′X, where X is generally a chlorine atom, a        bromine atom or an iodine atom and R′ is an aryl, alkyl,        substituted alkyl, substituted aryl or cycloalkyl group. A list        of the R′ groups which come within the invention is given, for        example, in the document WO 96/30421, from page 19, line 20, to        page 22, line 5, which is incorporated by reference.

Preferably, the controlled radical polymerization according to theinvention is carried out according to a reversible transfer byaddition-fragmentation of thiocarbonylthio compounds process.

Another subject matter of the invention is a process for the preparationof “second-generation” random microgels which comprises an additionalstage with respect to the preceding process consisting in adding, to themicrogel obtained in stage 1, at least one mono- or polyethylenicallyunsaturated monomer in the presence of an activator.

The activator depends on the method of controlled radical polymerizationused.

When use is made of a controlled radical polymerization process ofreversible transfer by addition-fragmentation of thiocarbonylthiocompounds type, then the activator is a source of free radicals as isdefined above.

When use is made of a controlled radical polymerization process of ATRPtype, then the activator is an organometallic catalyst.

This process results in the formation of homopolymers or blockcopolymers starting from the points of attachment of the control agentsto the first-generation microgel, which constitute the arms of thesecond-generation microgel.

Preferably, the monomer used in stage 2 is a monoethylenicallyunsaturated monomer as defined above.

Preferably, the controlled radical polymerization process used in stage2 is of reversible transfer by addition-fragmentation ofthiocarbonylthio compounds type.

Another subject-matter of the invention is a process for the preparationof “nth-generation” random microgels, which comprises an additionalstage with respect to the process for the preparation of“(n−1)th-generation” random microgels, consisting in adding, to the(n−1)th-generation microgel obtained, at least one mono- orpolyethylenically unsaturated monomer in the presence of an activator asdefined above.

n is an integer between 2 and 50, preferably between 2 and 10 and morepreferably still between 2 and 5.

Preferably, the monomer used in stage n is a monoethylenicallyunsaturated monomer as defined above.

Preferably, the controlled radical polymerization process used in stagen is of reversible transfer by addition-fragmentation ofthiocarbonylthio compounds type.

The process according to the invention can be carried out under bulk,solution, emulsion, dispersion or suspension conditions. Preferably, itis carried out under solution or emulsion conditions.

When it is carried out under solution, emulsion, dispersion orsuspension conditions, the solids content can be between 0.1% and 99%.The solids content is advantageously between 1 and 70% by weight, moreadvantageously still between 4 and 50% by weight.

The temperature can vary between ambient temperature and 150° C.depending on the nature of the source of free radicals and of thecontrol agents used.

Generally, the process is carried out in the absence of a UV source, bythermal initiation in the case of a controlled radical polymerizationprocess of reversible transfer by addition-fragmentation ofthiocarbonylthio compounds type or by redox initiation in the case of acontrolled radical polymerization process of ATRP type.

It is possible to adjust the properties of the microgels obtained byselecting specific monomers comprising ethylenic unsaturation and bychoosing the order or the method of introduction or the respectiveamounts of the monomers introduced.

For example, in the case of relatively unreactive control agents, it maybe advantageous to introduce the monomer or monomers continuously.

It is possible, by way of example, to provide combinations of neutralhydrophilic monomers with charged hydrophilic monomers exhibiting eitherpositive charges or negative charges.

It is also possible to provide combinations of hydrophilic monomers withhydrophobic monomers.

It is also possible to provide combinations of hard hydrophobic monomerswith soft hydrophobic monomers.

The term “hard monomer” is understood to mean a monomer resulting in apolymer with a glass transition temperature of greater than 20° C.

The term “soft monomer” is understood to mean a monomer resulting in apolymer with a glass transition temperature of less than 20° C.

It is also possible to vary the degree of branching, the number-averagemolar masses and the density of surface reactive functional groups andconsequently the shape and the size of said random microgels.

These molecular characteristics can be obtained by varying a certainnumber of experimental parameters, including the concentration of thereaction medium, the nature of the polymerization solvent, theproportion and the chemical nature of the polyethylenically unsaturatedmonomer, the proportion and the chemical nature of the control agent orthe polymerization temperature.

Another subject matter of the present invention is the microgels capableof being obtained by any one of the processes described above.

Another subject matter of the present invention is star-shaped polymerscapable of being obtained by a process for the preparation of annth-generation microgel, with n between 2 and 50, when the monomer(s)used in stage n is or are (a) monoethylenically unsatured monomer(s).

Thus, these star polymers are characterized in that they exhibit (1) acentral portion in the form of a first-generation microgel based on acrosslinked polymer resulting from the polymerization of the mono- andpolyethylenically unsaturated monomers and (2) arms composed of themonoethylenically unsaturated monomers only added starting from stage 2as defined above and comprising, at their end, the active part of thecontrol agent (—S(C═S)— functional group), in the case of a controlledradical polymerization process of reversible transfer byaddition-fragmentation of thiocarbonylthio compounds type, or thehalogen or pseudohalogen part, in the case of a controlled radicalpolymerization process of ATRP type.

Whatever the generation of the microgel, the active part of the controlagent (—S(C═S)— functional group), in the case of a controlled radicalpolymerization process of reversible transfer by addition-fragmentationof thiocarbonylthio compounds type, can be substituted in all or part bya hydrogen atom or a thiol functional group by employing processes knownto a person skilled in the art.

These processes consists of a cleavage stage, such as in particular thatdisclosed in the document WO 02/090424 and in Mori et al. in J. Org.Chem., 34, 12, 1969, 4170 (conversion of xanthate to thiol), oralternatively that disclosed by Udding et al. in the document WO02/090397 and in J. Org. Chem., 59, 1994, 6671 (conversion to thehydrogen atom).

The microgels according to the invention then exhibit chain ends basedon hydrogen atoms or on thiol functional groups, substituting in all orpart for the active part (—S(C═S)— functional group) of the controlagent.

The halogen chain ends resulting from the ATRP process can also bemodified chemically in various ways. Mention may be made, for example,of the dehydrohalogenation reaction in the presence of an unsaturatedcompound disclosed in patent WO 99/54365, which generates anunsaturation at the chain end. The halogen end can also be converted toother functional groups, for example by nucleophilic substitution orelectrophilic addition or alternatively by radical addition. All thesetechniques for the conversion of halogen chain ends are described in thedocument “Progress in Polymer Science (2001), 26(3), 337”.

The following examples illustrate the invention without, however,limiting the scope thereof.

EXAMPLES

In the examples given below, the polymerization reactions are carriedout under gentle flushing with nitrogen in glass reactors immersed in anoil bath preheated to a given temperature. The reactants are introducedin the following order: control agent, solvent, ethylenicallyunsaturated monomer(s), polyethylenically unsaturated monomer(s) andinitiator. Azobis(4,4′-cyanopentanoic acid) (ACP) is used as generatorof free radicals in the case where the polymerizations are carried outaccording to the process using control agents carrying thiocarbonylthiogroups or thiophosphate groups. The conversion of the monomer isevaluated by gravimetry or, if appropriate, by HPLC. The analysis of the(co)polymers is carried out by steric exclusion chromatography (SEC)using either THF or a water/acetonitrile (80%/20% by vol.) mixture aselution solvent. The number-average molar masses (M_(n)) and theweight-average molar masses (M_(w)) (g.mol⁻¹), expressed as polystyreneor poly(ethylene oxide) equivalents, and the distribution of the molarmasses, evaluated by the polydispersity index (I_(p)) corresponding tothe M_(w)/M_(n) ratio, are given here by way of indication.

These examples demonstrate that the use of appropriate amounts of thecontrol agent makes it possible to obtain polymers which are soluble inthe polymerization solvent, in comparison with the control experimentsinvolving the same reactants with the exception of the control agent. Infact, in this case, an insoluble gel is obtained. The control of thepolymerization is demonstrated in particular by the fact that thefirst-generation random microgels can be reactivated, acting aspolyfunctional cores during a subsequent polymerization stage. Thismakes it possible to generate second-generation random microgelscomposed of the core based on the first-generation random microgel andof polymer arms, the number-average molar mass of which increases withthe degree of conversion of the monomer.

Example 1 Synthesis of Random Microgels Based on Polyacrylamide which isPrepared from the Control Agent EtOC(═S)SCH(CH₃)COOCH₃

The polymerizations of the acrylamide are carried out at 70° C. in thepresence of N-methylene(bisacrylamide) (MBA) and of ACP for 4 hours.

Example 1.1

0.355 g (1.71×10⁻³ mol) of the xanthate EtOC(═S)SCH(CH₃)COOCH₃, 2.37 g(0.0333 mol) of acrylamide, 0.053 g (3.44×10⁻⁴ mol) of MBA and 0.099 g(3.53×10⁻⁴ mol) of ACP in a mixture comprising 9.1 g of deionized waterand 2.3 g of isopropanol are added. After reacting at 70° C. for 4hours, the characterization of the crude product by SEC in the aqueouseluent shows the absence of residual monomers and the presence of apredominant population with a molar mass at the tip of the peakcorresponding to M_(n)=1650 g.mol⁻¹.

Example 1.2

0.297 g (1.42×10⁻³ mol) of the xanthate EtOC(═S)SCH(CH₃)COOCH₃, 1.03 g(0.0142 mol) of acrylamide, 0.106 g (6.8×10⁻⁴ mol) of MBA and 0.070 g(2.5×10⁻⁴ mol) of ACP in a mixture comprising 4.2 g of deionized waterand 1.05 g of isopropanol are added. After reacting at 70° C. for 4hours, the characterization of the crude product by SEC in the aqueouseluent shows the absence of residual monomers. The SEC analysis resultsin the following values: M_(n)=1550 g.mol⁻¹ and I_(p)=3.45.

Example 1.3

0.047 g (2.25×10⁻⁴ mol) of the xanthate EtOC(═S)SCH(CH₃)COOCH₃, 1.64 g(0.0231 mol) of acrylamide, 0.036 g (2.33×10⁻⁴ mol) of MBA and 0.030 g(1.07×10⁻⁴ mol) of ACP in a mixture comprising 6.7 g of deionized waterand 1.7 g of isopropanol are added. After reacting at 70° C. for 4hours, a soluble product is obtained, the characterization of which bySEC in the aqueous eluent shows the absence of residual monomers.

Example 1.4

0.047 g (2.25×10⁻⁴ mol) of the xanthate EtOC(═S)SCH(CH₃)COOCH₃, 1.64 g(0.0231 mol) of acrylamide, 0.070 g (4.54×10⁻⁴ mol) of MBA and 0.030 g(1.07×10⁻⁴ mol) of ACP in a mixture comprising 6.7 g of deionized waterand 1.7 g of isopropanol are added. After reacting at 70° C. for 4hours, the characterization of the crude product by SEC in the aqueouseluent shows the absence of residual monomers. The SEC analysis resultsin the following values: M_(n)=6990 g.mol⁻¹ and I_(p)=22.3.

The examples which follow relate to the synthesis of second-generationrandom microgels starting from an aqueous solution of a first-generationrandom microgel described in examples 1.1 to 1.4. The polymerizationsare carried out at 70° C. for 15 hours, the concentration of thesolution being adjusted by addition of deionized water and with variableamounts of acrylic acid and of ACP being added. In these examples, thecontrolled nature of the polymerization reaction is demonstrated by thefact that the molar mass of the polymers increases as the amount ofacrylic acid added increases. It should be noted that the viscosities ofthe solutions obtained increase with increasing amounts of acrylic acidadded.

Example 1.5

0.34 g (4.72×10⁻³ mol) of acrylic acid, 0.7 g of deionized water and0.030 g (1.10×10⁻⁴ mol) are added to 2.21 g of the solution of thepolymer obtained in example 1.1 described above. A water-soluble productis obtained, the characterization of which by SEC in the eluent resultsin the following values: M_(n)=3610 g.mol⁻¹ and I_(p)=2.42.

Example 1.6

0.76 g (1.05×10⁻² mol) of acrylic acid, 1.1 g of deionized water and0.030 g (1.10×10⁻⁴ mol) are added to 2.08 g of the solution of thepolymer obtained in example 1.3 described above. A water-soluble productis obtained, the characterization of which by SEC in the eluent resultsin the following values: M_(n)=5080 g.mol⁻¹ and I_(p)=3.02.

Example 1.7

1.44 g (2.0×10⁻² mol) of acrylic acid, 1.8 g of deionized water and0.030 g (1.10×10⁻⁴ mol) are added to 2.04 g of the solution of thepolymer obtained in example 1.1 described above. A water-soluble productis obtained, the characterization of which by SEC in the eluent resultsin the following values: M_(n)=8400 g.mol⁻¹ and I_(p)=3.37.

Example 1.8

2.58 g (3.58×10⁻² mol) of acrylic acid, 2.9 g of deionized water and0.030 g (1.10×10⁻⁴ mol) are added to 2.14 g of the solution of thepolymer obtained in example 1.1 described above. A water-soluble productis obtained, the characterization of which by SEC in the eluent resultsin the following values: M_(n)=13 600 g.mol⁻¹ and I_(p)=11.29.

Example 1.9

0.48 g (6.66×10⁻³ mol) of acrylic acid, 0.8 g of deionized water and0.005 g (1.78×10⁻⁵ mol) are added to 2.02 g of the solution of thepolymer obtained in example 1.3 described above. A water-soluble productis obtained, the characterization of which by SEC in the eluent resultsin the following values: M_(n)=5620 g.mol⁻¹ and I_(p)=2.77.

Example 1.10

0.66 g (9.16×10⁻³ mol) of acrylic acid, 1 g of deionized water and 0.005g (1.78×10⁻⁵ mol) are added to 2.16 g of the solution of the polymerobtained in example 1.3 described above. A water-soluble product isobtained, the characterization of which by SEC in the eluent results inthe following values: M_(n)=7660 g.mol⁻¹ and I_(p)=3.25.

Example 1.11

1.31 g (1.81×10⁻² mol) of acrylic acid, 1.63 g of deionized water and0.005 g (1.78×10⁻⁵ mol) are added to 2.05 g of the solution of thepolymer obtained in example 1.3 described above. A water-soluble productis obtained, the characterization of which by SEC in the eluent resultsin the following values: M_(n)=11 240 g.mol⁻¹ and I_(p)=3.87.

Example 1.12

2.54 g (3.52×10⁻² mol) of acrylic acid, 2.86 g of deionized water and0.005 g (1.78×10⁻⁵ mol) are added to 2.09 g of the solution of thepolymer obtained in example 1.3 described above. A water-soluble productis obtained, the characterization of which by SEC in the eluent resultsin the following values: M_(n)=13 780 g.mol⁻¹ and I_(p)=5.90.

Example 2 Synthesis of Random Microgels Based on Butyl Acrylate which isPrepared from the Control Agent EtOC(═S)SCH(CH₃)COOCH₃

The polymerizations of the butyl acrylate are carried out at 75° C. inthe presence of MBA and of 2,2′-azobis-(2-methylbutyronitrile) (AMBN).

Example 2.1

0.625 g (3.0×10⁻³ mol) of the xanthate EtOC(═S)SCH(CH₃)COOCH₃, 15 g(0.117 mol) of butyl acrylate, 1.386 g (9×10⁻³ mol) of MBA and 0.1154 g(6.0×10⁻⁴ mol) of AMBN in 113 ml of ethanol are added. After reacting at75° C. for 5 hours, 0.0577 g (3.0×10⁻⁴ mol) of AMBN is added to thereaction medium. After heating for a further 5 hours, thecharacterization of the crude product by SEC in the THF eluent shows theabsence of residual monomers. The SEC analysis results in the followingvalues: M_(n)=9100 g.mol⁻¹ and I_(p)=3.2.

The examples which follow relate to the synthesis of second-generationrandom microgels starting from the solution of a first-generation randommicrogel described in example 2.1. The polymerization is carried out at75° C. for 10 hours, the concentration of the solution being adjusted byaddition of ethanol and with variable amounts of butyl acrylate and ofAMBN being added. In these examples, the controlled nature of thepolymerization reaction is demonstrated by the fact that the molar massof the polymers increases as the amount of butyl acrylate addedincreases. It should be noted that the viscosities of the solutionsobtained increase with increasing amounts of butyl acrylate.

Example 2.2

12 g (9.36×10⁻² mol) of butyl acrylate, 0.0154 g (8.0×10⁻⁵ mol) of AMBNand 17.53 of ethanol are added continuously over a period of 2 hours to18.074 g of the polymer solution obtained in example 2.1, which willhave been heated beforehand to 75° C. At the end of the continuousaddition, heating is maintained for a further 4 hours before theaddition of 7.690×10⁻³ mol) (4.0×10⁻⁵ g) of AMBN. After finally heatingfor a further 4 hours, the product obtained is analyzed by SEC in theTHF eluent and results in the following values: M_(n)=36 900 g.mol⁻¹ andI_(p)=2.9.

Example 2.3

24 g (1.873×10⁻¹ mol) of butyl acrylate, 0.0154 g (8.0×10⁻⁵ mol) of AMBNand 45.54 of ethanol are added continuously over a period of 2 hours to18.074 g of the polymer solution obtained in example 2.1, which willhave been heated beforehand to 75° C. At the end of the continuousaddition, heating is maintained for a further 4 hours before theaddition of 7.690×10⁻³ g) (4.0×10⁻⁵ mol) of AMBN. After finally heatingfor a further 4 hours, the product obtained is analyzed by SEC in theTHF eluent and results in the following values: M_(n)=48 600 g.mol⁻¹ andI_(p)=2.6.

1. A process for the preparation of first generation random microgelscomprising a step of controlled radical polymerization of a compositioncomprising at least one monoethylenically unsaturated monomer, at leastone polyethylenically unsaturated monomer, a source of free radicals,and a control agent, wherein said first generation random microgelscomprise a polymer having chain ends which can be activated byreversible transfer or by termination, said polymer comprising one ormore thiocarbonylthio groups.
 2. The process as claimed in claim 1,wherein the monoethylenically unsaturated monomer is: styrenederivatives, carboxylic acid vinyl esters, vinyl halides, vinylidenehalides, unsaturated ethylenic monocarboxylic acids, unsaturatedethylenic dicarboxylic acids, the monoalkyl esters thereof with alkanolshaving 1 to 4 carbon atoms, optionally N-substituted, amides ofunsaturated carboxylic acids, ethylenic monomers having a sulfonic acidgroup, an alkali metal or ammonium salts thereof, amides of vinylamine,unsaturated ethylenic monomers having a secondary, tertiary orquaternary amino group or a heterocyclic group having nitrogen,aminoalkyl (meth)acrylates, aminoalkyl(meth)acrylamides, zwitterionicmonomers, (meth)acrylic esters, vinyl nitriles, monomers having at leastone boronate functional group or a precursor thereof, phosphonatesmonomers comprising, N-methacrylamidomethylphosphonic acid esterderivatives, phosphate monomers, monomers having a —C—O—P— sequence incomparison with the —C—P— sequence of the phosphonates, and monomerscarrying an alkoxysilane group selected from the group consisting oftrimethoxysilypropyl methacrylate, triethoxysilylpropyl methacrylate,tributoxy-silylpropyl methacrylate, dimethoxymethylsilylpropylmethacrylate, diethoxymethylsilylpropyl methacrylate,dibutoxymethylsilylpropyl methacrylate, diisopropoxymethylsilylpropylmethacrylate, dimethoxysilylpropyl methacrylate, diethoxysilylpropylmethacrylate, dibutoxysilylpropyl methacrylate, diisopropoxysilyl-propylmethacrylate, trimethoxysilylpropyl methacrylate, triethoxysilylpropylmeth-acrylate, tributoxysilylpropyl methacrylate, trimethoxysilypropylacrylate, triethoxysilylpropyl acrylate, tributoxysilylpropyl acrylate,dimethoxymethylsilylpropyl acrylate, diethoxymethylsilylpropyl acrylate,dibutoxymethylsilylpropyl acrylate, diisopropoxymethylsilylpropylacrylate, dimethoxysilylpropyl acrylate, diethoxysilylpropyl acrylate,dibutoxysilylpropyl acrylate, diisopropoxysilylpropyl acrylate,trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate andtributoxysilylpropyl acrylate.
 3. The process as claimed in claim 2,wherein the monoethylenically unsaturated monomer is: α-methylstyrene,vinyltoluene, vinyl acetate, vinyl neodecanoate, vinyl propionate,acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaricacid, acrylamide, methacrylamide, N-methylolacrylamide,N-methylolmethacrylamide, N-alkylacrylamides, vinylsulfonic acid,vinylbenzenesulfonic acid, α-acrylamidomethylpropanesulfonic acid,2-sulfoethylene methacrylate, vinylformamide, vinylacetamide,N-vinylpyrrolidone, N-vinylcaprolactam, vinylpyridine, vinylimidazole,dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate,di(tert-butyl)aminoethyl acrylate, di(tert-butyl)aminoethylmethacrylate, dimethylaminomethylacrylamide,dimethylaminomethylmethacrylamide, sulfopropyl(dimethyl)aminopropylacrylate, glycidyl acrylate, glycidyl methacrylate, vinyl nitriles,acryloylbenzeneboronic acid, methacryloylbenzeneboronic acid,4-vinylbenzene-boronic acid, 3-acrylamidophenylboronic acid,3-methacrylamidophenylboronic acid, alone or as mixtures, or in the formof salts, n-propyl ester of N-methacrylamidomethylphosphonic acid,methyl ester of N-methacrylamidomethylphosphonic acid, ethyl ester ofN-methacrylamidomethylphosphonic acid, n-butyl ester ofN-methacrylamidomethylphosphonic acid, isopropyl ester ofN-methacrylamidomethylphosphonic acid, N-methacrylamidomethylphosphonicdiacid; N-methacrylamidoethylphosphonic acid dimethyl ester,N-methacrylamido-ethylphosphonic acid di(2-butyl-3,3-dimethyl) ester,N-methacrylamidoethylphosphonic diacid, N-acrylamidomethylphosphonicacid dimethyl ester, N-acrylamidomethylphosphonic acid diethyl ester,bis(2-chloropropyl) N-acrylamidomethylphosphonate,(N-acrylamidomethylphosphonic acid, di(n-propyl) vinylbenzylphosphonatedialkyl ester, di(isopropyl) vinylbenzylphosphonate dialkyl ester,diethyl vinylbenzylphosphonate dialkyl ester, dimethylvinylbenzylphosphonate dialkyl ester, di(2-butyl-3,3-dimethyl)vinylbenzylphosphonate dialkyl ester, di(t-butyl) vinylbenzylphosphonatedialkyl ester, vinylbenzylphosphonic diacid, diethyl 2-(4-vinylphenyl)ethanephosphonate, 2-(acryloyloxy)ethylphosphonic acid dimethyl ester,2-(methacryloyloxy)ethylphosphonic acid dimethyl ester,2-(methacryloyloxy)methyl-phosphonic acid diethyl ester,2-(methacryloyloxy)methylphosphonic acid dimethyl ester,2-(methacryloyloxy)propylphosphonic acid dimethyl ester,2-(acryloyloxy)methylphosphonic acid diisopropyl ester,2-(acryloyloxy)ethylphosphonic acid diethyl ester,2-(methacryloyloxy)ethylphosphonic acid,2-(methacryloyloxy)methylphosphonic acid,2-(methacryloyloxy)propylphosphonic acid,2-(acryloyloxy)propylphosphonic acid, 2-(acryloyloxy)ethylphosphonicacid; vinylphosphonic acid, optionally substituted by cyano, phenyl,ester or acetate groups, vinylidenephosphonic acid the sodium saltthereof, the isopropyl ester thereof, or bis(2-chloroethyl)vinylphosphonate.
 4. The process as claimed in claim 2,wherein the monoethylenically unsaturated monomer is a styrene monomer,vinyl ester, neutral or charged hydrophilic acrylate, hydrophobicacrylate, neutral or charged hydrophilic methacrylate, hydrophobicmethacrylate, hydrophilic or hydrophobic acrylamido derivatives, neutralor charged acrylamido derivatives, hydrophilic or hydrophobicmethacrylamido derivatives, or neutral or charged methacrylamidoderivatives.
 5. The process as claimed in claim 1, wherein thepolyethylenically unsaturated monomer is an organic compound reactive bythe radical route comprising at least two ethylenic unsaturations and atmost 10 ethylenic unsaturations.
 6. The process as claimed in claim 5,wherein the polyethylenically unsaturated monomer is an acrylic,methacrylic, acrylamido, methacrylamido, vinyl ester, vinyl ether,diene, styrene, .alpha.-methylstyrene or allyl derivative.
 7. Theprocess as claimed in claim 1, wherein the polyethylenically unsaturatedmonomer further bears one or more functional groups other than ethylenicunsaturations selected from the group consisting of hydroxyl, carboxyl,ester, amide, amino, substituted amino, mercapto, silane, epoxy and halofunctional groups.
 8. The process of claim 1, wherein thepolyethylenically unsaturated monomer is selected from the groupconsisting of divinylbenzene, vinyl methacrylate, methacrylic acidanhydride, allyl methacrylate, ethylene glycol dimethacrylate, phenylenedimethacrylate, diethylene glycol dimethacrylate, triethylene glycoldimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol200 dimethacrylate, polyethylene glycol 400 dimethacrylate,1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate,1,6-hexanediol dimethacrylate, 1,12-dodecanediol dimethacrylate,1,3-glycerol dimethacrylate, diurethane dimethacrylate ortrimethylolpropane trimethacrylate; vinyl acrylate, bisphenol A epoxydiacrylate, dipropylene glycol diacrylate, tripropylene glycoldiacrylate, polyethylene glycol 600 diacrylate, ethylene glycoldiacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate,tetraethylene glycol diacrylate, neopentyl glycol ethoxylate diacrylate,butanediol diacrylate, hexanediol diacrylate, aliphatic urethanediacrylate, trimethylolpropane triacrylate, trimethylolpropaneethoxylate triacrylate, trimethylolpropane propoxylate triacrylate,glycerol propoxylate triacrylate, aliphatic urethane triacrylate,trimethylolpropane tetraacrylate or dipentaerythritol pentaacrylate;vinyl crotonate, diethylene glycol divinyl ether, 1,4-butanediol divinylether or triethylene glycol divinyl ether; diallyl phthalate,diallyldimethylammonium chloride, diallyl maleate, sodiumdiallyloxyacetate, diallylphenylphosphine, diallyl pyrocarbonate,diallyl succinate, N,N′-diallyltartardiamide,N,N-diallyl-2,2,2-trifluoroacetamide, the allyl ester ofdiallyloxyacetic acid, 1,3-diallylurea, triallylamine, triallyltrimesate, triallyl cyanurate, triallyl trimellitate or1,3,5-triallyltriazine-2,4,6(1H,3H,5H)-trione;N,N′-methylenebisacrylamide, N,N′-methylenebismethacrylamide,glyoxalbisacrylamide or diacrylamidoacetic acid; divinylbenzene and1,3-diisopropenylbenzene; butadiene, chloroprene or isoprene.
 9. Theprocess as claimed in claim 1, wherein the polyethylenically unsaturatedmonomer is N,N′-methylenebisacrylamide, divinylbenzene, ethylene glycoldiacrylate or trimethylolpropane triacrylate.
 10. The process as claimedin claim 1, wherein the polyethylenically unsaturated monomers withrespect to the monoethylenically unsaturated monomers are in a molarfraction of between 0.001 and
 1. 11. The process as claimed in claim 10,wherein the molar fraction of polyethylenically unsaturated monomerswith respect to the monoethylenically unsaturated monomers is between0.01 and
 1. 12. The process as claimed in claim 1, wherein thecontrolled radical polymerization is carried out according to a AtomTransfer Radical Polymerization (ATRP) process or by a reversibletransfer by addition-fragmentation of thiocarbonylthio compoundsprocess.
 13. The process as claimed in claim 12, wherein the controlledradical polymerization is carried out according to a reversible transferby addition-fragmentation of thiocarbonylthio compounds process.
 14. Theprocess as claimed in claim 13, wherein the thiocarbonylthio compoundsare compounds of following formula (A):

wherein: Z represents: a hydrogen atom, a chlorine atom, an optionallysubstituted alkyl radical or an optionally substituted aryl radical, anoptionally substituted heterocycle, an optionally substituted alkylthioradical, an optionally substituted arylthio radical, an optionallysubstituted alkoxy radical, an optionally substituted aryloxy radical,an optionally substituted amino radical, an optionally substitutedhydrazine radical, an optionally substituted alkoxycarbonyl radical, anoptionally substituted aryloxycarbonyl radical, a carboxyl or optionallysubstituted acyloxy radical, an optionally substituted aroyloxy radical,an optionally substituted carbamoyl radical, a cyano radical, a dialkyl-or diaryl-phosphonato radical, a dialkyl-phosphinato ordiaryl-phosphinato radical, or a polymer chain, and R₁ represents: anoptionally substituted alkyl, acyl, aryl, aralkyl, alkenyl or alkynylgroup, an optionally substituted, aromatic, saturated or unsaturated,carbon ring or heterocycle, or a polymer chain.
 15. The process asclaimed in claim 12, wherein the thiocarbonylthio compounds arexanthate, dithiocarbamate or dithioester compounds carrying a singlefunctional group of formula —S(C═S)—.
 16. The process as claimed inclaim 15, wherein the compounds are xanthates.
 17. A process for thepreparation of second-generation random microgels, comprising the stepsof: 1) preparing a first-generation random microgel wherein saidpreparation comprises a step of controlled radical polymerization of acomposition comprising at least one monoethylenically unsaturatedmonomer, at least one polyethylenically unsaturated monomer, a source offree radicals, and a control agent, and 2) adding at least one mono- orpolyethylenically unsaturated monomer to the microgel obtained instep 1) in the presence of an activator;  wherein said first generationrandom microgels comprise a polymer having chain ends which can beactivated by reversible transfer or by termination, said polymercomprising one or more thiocarbonylthio groups and said secondgeneration random microgels comprise a core of a first generation randommicrogel and polymer arms extending from the chain ends which can beactivated by the central portion.
 18. A process for the preparation ofnth-generation random microgels, n being an integer between 3 and 50,comprising the steps of: a) preparing a first-generation randommicrogel, wherein said preparation comprises a step of controlledradical polymerization of a composition comprising at least onemonoethylenically unsaturated monomer, at least one polyethylenicallyunsaturated monomer, a source of free radicals, and a control agent, b)preparing an 2nd generation random microgel by adding, in the presenceof an activator, at least one mono- or polyethylenically unsaturatedmonomer to the first-generation microgel obtained in step a) in thepresence of an activator to form a 2nd generation random microgel; c)preparing a next generation random microgel by adding in the presence ofan activator at least one mono- or polyethylenically unsaturated monomerto the previous generation random microgel, where the step is performedn−2 times to form and (n−1)th generation random microgel; and d)preparing an nth generation random microgel by adding in the presence ofan activator at least one mono- or polyethylenically unsaturated monomerto the (n−1)th generation random microgel obtained at the end of step c)in the presence of an activator.
 19. The process as claimed in claim 17,wherein the activator is a source of free radicals.
 20. The process asclaimed in claim 17, wherein the monomer(s) used in step 2 is or are (a)monoethylenically unsaturated monomer(s) in order to obtain astar-shaped polymer.
 21. The process as claimed in claim 18, wherein themonomer(s) used in step n is or are (a) monoethylenically unsaturatedmonomer(s) in order to obtain a star-shaped polymer.
 22. The process asclaimed in claim 21, wherein the star-shaped polymer exhibits (1) acentral portion in the form of a first-generation microgel based on acrosslinked polymer resulting from the polymerization of the mono- andpolyethylenically unsaturated monomers and (2) arms composed of themonoethylenically unsaturated monomers only added starting from step 2and comprising, at their end, an active part of the control agent(—S(C═S)— functional group), in the case of a controlled radicalpolymerization process of reversible transfer by addition-fragmentationof thiocarbonylthio compounds type, or the halogen or pseudohalogenpart, in the case of a controlled radical polymerization ATRP process.23. The process as claimed in claim 22, wherein the active part of thecontrol agent (—S(C═S)— functional group) is substituted in all or partby a hydrogen atom or a thiol functional group.